A study on the differential impacts of ENSO and IOD on the interannual air temperature variability over Sri Lanka^*

Previous studies on the interannual climate variability in Sri Lanka have primarily focused on precipitation characteristics, while the understanding of the interannual variability of air temperature and its climatic drivers remains limited. This study analyzes the interannual variability of surface air temperature over Sri Lanka and its influencing factors based on high-resolution climate reanalysis data and interannual climate indices of the tropical Indian-Pacific Ocean. The results indicate that the air temperature across Sri Lanka exhibits relatively consistent interannual fluctuations, with larger amplitude variations north of the central highlands and smaller changes in coastal areas. Partial correlation analysis reveals that the interannual variability of air temperature in Sri Lanka is significantly regulated by the El Niño-Southern Oscillation (ENSO), while the influence of the local Indian Ocean Dipole (IOD) is not significant. Further partial regression analysis shows that during El Niño events, the Indian Ocean basin warms as a whole, continuously heating the surrounding atmosphere and affecting air temperature. Meanwhile, enhanced shortwave radiation in the tropical southeastern Indian Ocean and the Bay of Bengal leads to significant land warming, further heating the near-surface air through sensible heat exchange. In contrast, during positive IOD events, the air temperature pattern shows cold anomalies in the eastern Indian Ocean and the Bay of Bengal, and warm anomalies in the western Indian Ocean and the Arabian Sea. As Sri Lanka is located at the transitional zone between these warm and cold anomalies induced by IOD, the net temperature response is relatively weak. These findings enhance the understanding of interannual climate variability in Sri Lanka and its surrounding regions and provide a scientific reference for addressing climate risks such as extreme heat events.